Voigt pipes and MLTL - how they work?! Which will fit my room?!

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  • เผยแพร่เมื่อ 22 ส.ค. 2024
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ความคิดเห็น • 83

  • @earlfenwick
    @earlfenwick ปีที่แล้ว +3

    It remind me of discovering as a kid that I could make huge waves in a swimming pool by pushing a small kick board up and down at just the right frequency.

  • @Soundesprit
    @Soundesprit ปีที่แล้ว +4

    The real explanation about low frequency attenuation in small rooms is the cancellation effect when waves resonances of your room hits the back of the cone driver via the mouth of the pipe. A mass load can help to minimize this effect, as its react as a buffer. On the other side this effect is a self healing process to cancel room resonances.

    • @realworldaudio
      @realworldaudio  ปีที่แล้ว +1

      Exactly! 👍👍 And that's also the reason why the amplifier choice is critical, and why high DF amps might not work well, as they try to counteract this interaction...

  • @steveducell2158
    @steveducell2158 ปีที่แล้ว +5

    I have built a pair of Frugal Horns XL and enjoy them but I was not getting the bass response that everyone talks about. Thanks, to your videos I now have a greater understanding of the Voigt pipe and its strengths and limitations. Thank you so much.

    • @realworldaudio
      @realworldaudio  ปีที่แล้ว +2

      Hi Steve, with horns and pipes a lot rides on the room interaction to form bass, as the low frequencies are not created by pressurization. Also, the amp - speakers relationship is super critical as well, you might get zero bass with one and thunderous with another.

  • @a.x.marcus4627
    @a.x.marcus4627 ปีที่แล้ว +2

    Janos, this is excellent stuff and very well explained. Thank you.

  • @davebutler3905
    @davebutler3905 2 หลายเดือนก่อน

    Excellent information.
    Thank you!

  • @I.am.KubKab
    @I.am.KubKab หลายเดือนก่อน

    Thank you Janos.

  • @geraldhaller9906
    @geraldhaller9906 ปีที่แล้ว +3

    Ich mag den Sound von TQWT Lautsprechern sehr besonders dann wenn dort ein Breitbänder arbeitet .Voigt Pipes sind mir zu groß genauer zu hoch da kommt man schnell auf über 2 m Höhe wenn man etwas größere Chassis nutzen möchte mit mehr als 4"-5" .
    Aktuell baue ich zur zeit eine TQWT Box mit 6" Tang Band w6 2144 die ist nun ca 1,3m groß und hätte eigentlich noch größer gedurft mit ca 1,45 m wäre sie mir aus optischen gründen zu groß geworden aber auch aus praktischen Gründen denn man muss sie auch handhaben können .
    Als Voigt Pipe wäre sie vermutlich über 2,5m hoch geworden und das bei einer Deckenhöhe von 2,52 m verdammt knapp so knapp das man sie nicht aufstellen oder hinlegen könnte .

    • @realworldaudio
      @realworldaudio  ปีที่แล้ว +1

      Voigt pipe funktionieren gut, wenn sie so hoch wie möglich sind, obwohl ich die Höhe aus praktischen Gründen auf 2 m begrenze. Mit dem Cube Audio Fc8 ist alles, was benötigt wird, die mittel und tiefe Bass sind fantastisch stark und klar. Viel Glück für Ihr nächstes Projekt! Entschuldigung für mein schlechtes Deutsch. János

    • @geraldhaller9906
      @geraldhaller9906 ปีที่แล้ว +1

      @@realworldaudio Dein Deutsch ist perfekt besser als mein Englisch .
      Dessen bin ich mir schon einigermaßen bewusst das die besser klingen je größer sie sind (höher) das habe ich auch bei den TQWT Gehäusen festgestellt das die schöner klingen wenn ich sie möglichst groß baue . so klingt die mit dem 3" Breitbänder fast genauso schön wie die mit dem 6" Breitbänder da ich die kleine im Verhältnis zur großen größer gebaut habe mit ca 1m zu 1,3 m werde aber nochmal ein grö0eres Gehäuse für den 6" Breitbänder bauen um dann endgültig den Vergleich zu haben wie sehr die Baugröße (Länge des Kanals ) den klang beeinflusst und in wie fern dies Einfluss nimmt .
      Bei der Dämmung bin ich mir noch nicht so sicher wie sehr diese den Klang beeinflusst denke nicht so gewaltig wie oft behauptet wird .

    • @vladimirk4461
      @vladimirk4461 3 หลายเดือนก่อน

      Попробуйте динамик sica 12d, очень хороший динамик по звуку и чувствительность отличная).

  • @sjhorton1184
    @sjhorton1184 ปีที่แล้ว +2

    So I had a bit of a revealation when building my Frugal Horn Lites and they are basically a single fold Voigt pipe like you have drawn, but with the drive flipped to the "back" and then with curved sweeps added to the port, extending it into a type of horn-ish output. Quite smart.

    • @realworldaudio
      @realworldaudio  ปีที่แล้ว +1

      Scott, what was that revelation? 👍✨

  • @asadabbasmirza9519
    @asadabbasmirza9519 6 หลายเดือนก่อน +1

    Super presentation.

  • @sonhouse9636
    @sonhouse9636 2 หลายเดือนก่อน

    Great video! Many rhanks!

  • @linandy1
    @linandy1 ปีที่แล้ว +1

    Wow, i have enough room for one of those. I must try it. I want quality bass

    • @realworldaudio
      @realworldaudio  ปีที่แล้ว +1

      Good luck, it will be a fun project! These speakers project bass in a very different way from typical box speakers. ;

  • @MiracleManMatt
    @MiracleManMatt 4 หลายเดือนก่อน +1

    Brilliant explanation!

  • @anandshah71
    @anandshah71 ปีที่แล้ว +2

    This is probably the best video Janos that I wanted to see thank you. I have a 27ft depth room and will make both type boxes and hear the difference
    I have tang band 1808 and SB20FRPC30
    Any idea on the internal damping u suggest and crossover ?

    • @realworldaudio
      @realworldaudio  ปีที่แล้ว +1

      Try light stuffing in the top section, and just a single small capacitor for the tweeter, running the main driver full range.

  • @earkivaren
    @earkivaren 2 ปีที่แล้ว +1

    Fantastic video Janos!

    • @realworldaudio
      @realworldaudio  2 ปีที่แล้ว

      ✨👍

    • @earkivaren
      @earkivaren 2 ปีที่แล้ว

      Just plowing my way through the VP playlist to pick up all the aspects and details of the VPs themselves and how to build a pair. Thanks as always! Claus

  • @1moderntalking1
    @1moderntalking1 2 ปีที่แล้ว +1

    Wow great explanation thanku

  • @balintkekedi
    @balintkekedi 2 ปีที่แล้ว +1

    Hi János, excellent video, thank you. I am considering to build a pair of Voigt pipes one day, and I understood the requirements in terms of room dimensions to get the best out of them. However, I am still unsure whether our flat is a suitable place for such speakers, I'll try to do my best in describing it, for the lack of ability to upload a floor plan here. So the living room is only 4.84 x 4.25 m, the hifi is on the long wall (it can'tbe elsewhere). Just next to it, on the short wall, there is the kitchen. The kitchen is open towards the living room across its full width (2.6m, with a large, 4-wing door that is always open), leaving only a smaller portion to the wall potentially blocking/reflecting the sound waves. Then, after the kitchen, there is the bedroom, separated by another relatively big double door (which is most of the time open). Those 3 rooms (living room + kitchen + bedroom) constitute a 12.3 m long "channel" or "tube", if you like, which is 1.2m at its narrowest section (the bedroom door), but most of the time, it's wider. Like I said, the speakers are on the long wall of the living room, so in front of them, there is only 4.25 m to the other wall, but the whole system is on one end of this 12.3 m long space (the long axis extends to the right side from the speakers: living room -> kitchen -> bedroom). The ceiling is 3m high in all of the rooms. Could that space and set-up possibly work well with Voigt pipes in your opinion? Thank you in advance!

    • @realworldaudio
      @realworldaudio  2 ปีที่แล้ว +2

      Hello Bálint, that's sadly the situation that tends to cripple Voigt pipes, or makes the amplifier choice critical. (Can;t make a generic amp recommendation, as the actual synergy between room-driver-amp will matter, and that's relatively unpredictable until tested). I have a similar situation in my living room downstairs, and my Fostex FE204 Voigt pipes did not work there with my amplifiers. Well, they did make sound and not bad at that... yet it was but a faint shadow of what they are capable of in a balanced room.
      To make a Voigt pipe work in such a setting you will need a driver with a high Qts (such as the Cube audio Fc8, but all the Fostex drivers are off the menu), or have a very specific amplifier - speakers match. For example, in my case, with the Fostex FE204 VP they were completely OK in that unbalanced room setting when matched with a Quicksilver Triode amplifier. (However, no other SE/PP amplifier nor solid state made it work - everything rolled off basically around 200Hz!)
      There's one thing you might try.... build the Voigt pipes and if you don't get enough bass, then convert it to slot port bass reflex cabinet. Will look like a Voigt pipe, but with a port instead of the mouth. I have done this, and this can / will make the cabinet generate bass in rooms / amplifier choices that do not support quarter wave operation.

    • @balintkekedi
      @balintkekedi 2 ปีที่แล้ว +1

      @@realworldaudio, thank you, János, for your quick and honest response. In that case, I might just continue to further tweak the speakers I have, which are a sealed box design (in my limited experience, I have preferred sealed boxes to ported ones so far). I have already replaced the built-in crossover with external ones, as you too suggested in another video, and it yielded a great improvement. I guess I could try to make live cabinets instead of the current MDF boxes, as a sort of ultimate mod. My understanding is that such a move would entail the redesigning of the crossover network. Would you be willing to discuss a few questions by email as well? 😊

    • @realworldaudio
      @realworldaudio  2 ปีที่แล้ว

      @@balintkekedi Szervusz Bálint, you can write me at: arcturus127@ gmail.com ;

  • @sc0or
    @sc0or 5 หลายเดือนก่อน

    In an ideal case we need both: pressurized and energized lows. Because there are drums and organs. I think a 8" fullranger is not able to do that. We need a 18" woofer.

  • @mikesaunders4694
    @mikesaunders4694 2 ปีที่แล้ว +2

    Thanks Janos….you have a way of getting these concepts across in an easy to understand way. So what’s your recommendation for the best cabinet type for a full range driver 8” driven by flea power in a small room 4x3.5m. I’m thinking of experimenting with a diy bass reflex or a Gilbert Briggs style distributed port cabinet.

    • @realworldaudio
      @realworldaudio  2 ปีที่แล้ว +2

      Hi Mike, the bass reflex will work very well. I warmly recommend to use slot ports - can be dual port, just make it slotted. Avoid the plastic PVC pipe tube! 🤣🤣

  • @danbuffington75
    @danbuffington75 2 ปีที่แล้ว +4

    Which type is the Pearl Accoustics Sibelius? They sell for something like $5k per pair. Built by a classical music sound engineer, I think. I know they tuned it in a studio using actual instruments to voice them. No crossover.

    • @frankgeeraerts6243
      @frankgeeraerts6243 2 ปีที่แล้ว +3

      I never listened to that speaker but I agree with the philosophy..

    • @realworldaudio
      @realworldaudio  2 ปีที่แล้ว +2

      They re transmission lines. Have not seen the insides, so cannot be more specific than that - basically, they are a kind of Voigt pipe, could be MLTL, we would need to see the insides ; ).

    • @TheZpilot55
      @TheZpilot55 2 ปีที่แล้ว

      Please watch this video, if allowed by YT th-cam.com/video/_XrzkkRARNo/w-d-xo.html
      and see plans here: frugal-phile.com/boxlib/pensils/Pensil103-plan-300114.pdf

  • @neusprach
    @neusprach 9 หลายเดือนก่อน

    Very informative. Thanks for sharing!

  • @hoobsgroove
    @hoobsgroove 2 ปีที่แล้ว +2

    yes but the Fostex drivers are known for the lack of bass.
    do you not have an improvement now with cube drivers.
    and another thing if you put it close to the wall and tilt it back will give you more bass
    plus if you put a board on the inside of the port 4" -5" long should get you down to 30 Hz ish. plus if the front baffle is wider will increase lower frequencies for an 8" driver 15" across. just put a board on the front.

    • @realworldaudio
      @realworldaudio  2 ปีที่แล้ว +1

      Yes, the Fc8 has quite a bit more bass output. Although I have to add that the FE204 has excellent bass when positioned properly, in a room that has the length to support it: the FE204 had strong bass down to 30Hz!
      The Fc8 went down to clear 25Hz last night! Significant step-up. ;

    • @hoobsgroove
      @hoobsgroove 2 ปีที่แล้ว

      @@realworldaudio right just listening to this you're probably like it acid folk she's got a nice voice th-cam.com/video/zlG8QUEPWwY/w-d-xo.html

  • @NickP333
    @NickP333 2 ปีที่แล้ว +3

    This was such a fantastic video, Janos. Thank you. Now, would an MLTL cabinet work with a driver and a compression tweeter, or is a full range driver the optimal way to make that type of cabinet really sing? Also, wouldn’t a very small slotted port work better than a small circular one? Again, many thanks for this video. It was extremely helpful. 😊🔊🎶🐱

    • @realworldaudio
      @realworldaudio  2 ปีที่แล้ว +2

      The VOL is effectively a derivation on MLTL ; ). So yes, the woofer by itself can benefit tremendously from MLTL. And, slotted port better for MLTL than circular one... can be big, not just small. The wider, the better. Keep it as wide as the cabinet, so the air flow is laminated and the turbulence is restricted to 1 dimension instead of 2 with the circular & undersized ports. ; ).

    • @NickP333
      @NickP333 2 ปีที่แล้ว +2

      @@realworldaudio Thanks a ton for this information. That’s what I will most likely do. I think my drivers and tweeters should should work well in that type of cabinet. A million thanks again, Janos! 👍🎶🔊🎶

  • @johnkipos1427
    @johnkipos1427 ปีที่แล้ว +1

    Interesting design
    As far as finding a driver Fullrange
    It’s hard finding one that doesn’t have break up & lots of rigging .
    Not any information on spectral decays
    Even the exotic drivers
    Do you recommend any?
    Also do you show these measurements

    • @realworldaudio
      @realworldaudio  ปีที่แล้ว

      This is so frustrating! I posted reply twice, and YT deleted them both times. :( I wonder if this post will show up...

  • @joelam2328
    @joelam2328 ปีที่แล้ว +2

    Hi Janos, Trying to understand the difference between having the voigt pipe opening facing the front as they normally do, or like the Cube Audio speaker enclosure (e.g. Nenuphar) that have the pipe opening at the bottom of the cabinet facing the floor. What is the difference and any advantage of one over the other?
    Is it correct that the internal volume of the voigt pipe should be equal to or larger than Vas of the driver? Thanks.

    • @realworldaudio
      @realworldaudio  ปีที่แล้ว +1

      Hi Joe, the Voigt pipes break the Vas rules to a degree, as the opening is so big that the driver literally works with the whole room, not just the internal volume. For example, my Voigt pipes internal volume is way smaller than the Vas of the CA Fc8.
      Front port or floor port - there are several differences, but the main one is you will benefit more of the floor port when you have a hard floor. If you have carpet underneath, then the floor port is catastrophic as the waves get very heavily dampened and the sound collapses. Ultimately that's the key difference between the two.

  • @vlkrwst
    @vlkrwst ปีที่แล้ว

    Hi Janos, thanks so much for your work and letting us participate. How much of a difference would it make if you'd switch the position of the driver by 90 degrees in a folded pipe on the sidewall of the cabinet? I was wondering if you could put it directly on the wall. Best regards

  • @asadabbasmirza9519
    @asadabbasmirza9519 6 หลายเดือนก่อน

    V v good

  • @summersong88
    @summersong88 2 ปีที่แล้ว +2

    Hi Janos, thanks for this video series, I’m watching each one with much anticipation. Now my room is 2.7x3.8m. I had been planning of building a voigt pipe using Faital Pro 4FE32 (4 inch, 91dB/W/m, Qts 0.61) but after watching this video I’m afraid my room won’t support the wavelength needed for bass. 3.8m is about 100Hz wavelength. For my room would you say a well designed ported enclosure on a stand would be better? Thank you once again!

    • @realworldaudio
      @realworldaudio  2 ปีที่แล้ว +1

      With that high Qts I think you can make it work, although I never tried such high Qts driver in a Voigt pipe, but it should work as the high Qts is very helpful to support bass when the room is smaller than optimal.

    • @summersong88
      @summersong88 2 ปีที่แล้ว +1

      @@realworldaudio Thank you so much, I think it is worth trying then.

  • @Drunken_Hamster
    @Drunken_Hamster ปีที่แล้ว +2

    Can you combine a very large Voigt pipe (IE one built for a 12-inch driver) with something like a DML panel for the ultimate natural full-range response regardless of whether or not you're on axis?

    • @realworldaudio
      @realworldaudio  ปีที่แล้ว +1

      Enlarging the front baffle will improve the upper&midbass fullness if needed, an is a fantastic help for low Qt drivers, and onces that can use a lift in that region. With the Cube Audio Fc8 though it's not needed, and it has the best off axis response I ever heard of any loudspeaker. No sudden transition of character, or image when I shift positions or walk around the room, it is just like having musicians in the room and walking around. Virtually identical experience with the freedom of picking where I listen.

  • @RainerKormann
    @RainerKormann 7 หลายเดือนก่อน +1

    Hi Janos, thank you very much for your very helpful explanations. As I understand you: The biggest dimension in my Room is 5 m, so I would tune the VP to 34 Hz (half a wavelength). But what about the distance between my listening position and die VP? Can I really tune the VP by the room-dimension or do I have to tune it for the distance between me and the VP?

    • @realworldaudio
      @realworldaudio  7 หลายเดือนก่อน

      That tuning / room size will work extremely well. About the listening position: there is no restraint on the listening position! When the pipes are set up well, you can sit, stand, or lie down anywhere, or even go to next room, it will appear as if there's live music in the room, and the listening position does not impact it. Of course you will experience changes based on the rooms acoustic properties, but it will affect the sound as the room affects instruments played in the room, and when people speak in the room - it will just sound natural vs the great/disappointing dichotomy of most audiofile speakers.

  • @acuben65
    @acuben65 ปีที่แล้ว

    Hi, thanks for sharing your wise and wide experience. Is bracing, mainly the front baffle, useful or not? Is thickness of the walls important? Do voigt pipes need cancelation stuffing as for other tl?
    Many thanks….

  • @tukangbox2020
    @tukangbox2020 ปีที่แล้ว

    👍👍👍

  • @TitofBee
    @TitofBee ปีที่แล้ว

    cool video broo

  • @dannixon247
    @dannixon247 2 ปีที่แล้ว +1

    Excellent talk as always J.
    So is that why some pro audio Sub manufacturers test out doors on a tower? (Presumably because an anechoic chamber for say 20Hz would be silly huge and spendy)

    • @realworldaudio
      @realworldaudio  2 ปีที่แล้ว +1

      Thank you Dan! Correct, they elevate the sub to simulate an anechoic response... quite useless for the user though. How many subs are placed on a stand at home ? : ) Nevertheless, the quasi-anechoic response gives ideas that they can use to standardize and for quality control.

    • @virenk859
      @virenk859 ปีที่แล้ว

      ​​@@realworldaudio Why is it only Bass that is talked about? There are many more aspects of music that need to be reproduced.. Is it because that's how Americans like it? Americans like anything that is bigger than what their friends have... They don't want the best, they want the biggest😂😂 Reminds me of Kindergarten 😅

  • @adrianosparlapipas
    @adrianosparlapipas ปีที่แล้ว

    So what Real World Audio actually saying (at 15:45) is that a hole might be better instead of a rectangular opening. What if we go inbetween size? not too big not to small?

    • @realworldaudio
      @realworldaudio  ปีที่แล้ว

      It totally depends on your room. The smaller the room, the smaller opening will be most optimal. 👍

  • @ColocasiaCorm
    @ColocasiaCorm 10 หลายเดือนก่อน +1

    Janos can full range drivers convincing ply reproduce full scale orchestra

    • @realworldaudio
      @realworldaudio  10 หลายเดือนก่อน

      Yes, it is possible. A few dB quieter than the live orchestra though, but it would not be an issue unless someone already has serious hearing problems and needs to blast just to hear / feel anything. Then they will not work for orchestra.
      I have listened to orchestra on the Voigt pipes many times right after going to the symphony, and I found their rendering quite realistic, so much so as I did not feel I was missing out on anything.

  • @ArnoldteRaa
    @ArnoldteRaa 2 ปีที่แล้ว +1

    Great video again! Could one say the VOL is pressurised? As the bass reflex has chaos inside and the slot is tuned?

    • @realworldaudio
      @realworldaudio  2 ปีที่แล้ว +1

      Great observation! Yes, it is slightly pressurized! Compared to a regular cabinet, we are talking a few percents in comparison. If we wre comparing it to bench pressing then it would be benching 200kg with a typical BR cabinet, and benching 10kg with the VOL. (Instead of breaking the back, we are not even breaking a sweat ; ).
      In a typical BR cabinet under 800Hz there is total chaos, so the entirety of bass and the lower midrange energies are out of whack. Inside the VOL cabinet down to 40Hz there is order. Only the frequencies under 40Hz cause chaos - and these are the ones that get shunted through the slot into the room. So yes, it could be better if the cabinet could support down to let's say 10Hz - but then it would be unrealistically giga-enormous. Hence, I cut the "most reasonable compromise, that pushes the boundaries as far as possible while allowing a cabinet that fits in my living room. (Also, this is the configuration that the driver prefers the most - going for a longer transmission line would need multiple woofers per cabinet, and I would need not a living room but a hall or theatre to house them!)

  • @lordgothington
    @lordgothington ปีที่แล้ว

    Can the room be too big? What happens if you use them outdoors? Sounds like maybe you get the lowest frequencies, but a bit less SPL?

    • @realworldaudio
      @realworldaudio  ปีที่แล้ว

      I have never tried them outdoors. However, going for different size rooms and outdoors is a MASSIVE change. Each scenario requires a VASTLY different loudspeaker build. Just think of loudspeakers that they MUST match the room. Like shoe size and feet. Otherwise it does not work. Yes, do do get sound but the range is exceptional sound in a matching room vs very poor sound in a non-matching room - for the very same loudspeaker.
      Also outdoors you get a lot less SPL, not just a bit less. That's why event PA systems have such difficulties, and it's a major feat to produce deep bass outdoors.

  • @asadabbasmirza9519
    @asadabbasmirza9519 6 หลายเดือนก่อน

    So there is no difference in folded voight pipe? For the room?

  • @abramperez3480
    @abramperez3480 4 หลายเดือนก่อน

    but where do you place the pipes and where do you sit?

  • @matereo
    @matereo ปีที่แล้ว +1

    Have you ever tried Sonido drivers?

    • @realworldaudio
      @realworldaudio  ปีที่แล้ว

      No, but I really warmly recommend them.

  • @asadabbasmirza9519
    @asadabbasmirza9519 6 หลายเดือนก่อน

    Change in size of port????

  • @asadabbasmirza9519
    @asadabbasmirza9519 6 หลายเดือนก่อน

    4 inch driver???

  • @raynerstuelgalid
    @raynerstuelgalid ปีที่แล้ว

    Any software to model a full Voigt Pipe enclosure? Thanks.

    • @realworldaudio
      @realworldaudio  ปีที่แล้ว +1

      I have stayed away from software models. I'd really recommend to use a cabinet that has been used successfully, as a software jut gets you in the ballpark, but it can also lead you t a very bad place without knowing it. That's why it's important to build something that someone has already proven it works, and then take from there, fine tune it to your room, placement options, system, preferences.
      There are models out there though. Eduard Brokeman has on his channel a video dedicated to a comprehensive speaker modeling software that does transmission line and TQWP simulation. That is very good, but really complex. You will have to dig in very deep, and still will face the issue that you will not know what is the right call to make. I fnd the simulations useful for when you already have your speakers, you re not happy about some aspect and trying to find what can be wrong that needs fixing. That's where the simulations will help. 👍🎶🎶

    • @johnhudelson2652
      @johnhudelson2652 4 หลายเดือนก่อน +1

      There is hornresp, that you enter in the driver parameters and you specify cross sections and their lengths. The software then plots response cuves.

  • @davebutler3905
    @davebutler3905 2 หลายเดือนก่อน

    Talking of cluster fucks... I'm no expert, but resonance is a very tight band of frequency. If you hold down the sustain pedal on a piano, only the string that is precisely matched to whatever note you play or sing will sympathetically vibrate.
    In your hifi situation, you have the natural resonances of the room. The driver and the enclosure, all making narrow peaks in the excitability of the air. Air temperature and atmospheric pressure will also vary the exact frequencies of all these.
    Trying to compensate for driver resonance by introducing an enclosure resonant frequency seems like rolling a second cheese down the hill to fetch the one you dropped.